Design notes for the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 14
Recommended pin connections
The only required pin connections are VCC, GND, DOUT and DIN. To support serial firmware updates,
VCC, GND, DOUT, DIN, RTS, and DTR should be connected.
All unused pins should be left disconnected. All inputs on the radio can be pulled high with internal
pull-up resistors using the PR software command. No specific treatment is needed for unused
outputs.
Other pins may be connected to external circuitry for convenience of operation including the
Associate LED pin (pin 15). The Associate LED will flash differently depending on the state of the
module.
If analog sampling is desired, VRef (pin 14) should be attached to a voltage reference.
Board layout
XBee modules are designed to be self sufficient and have minimal sensitivity to nearby processors,
crystals or other PCB components. As with all PCB designs, Power and Ground traces should be
thicker than signal traces and able to comfortably support the maximum current specifications. No
other special PCB design considerations are required for integrating XBee radios except in the
antenna section.
Antenna performance
Antenna location is an important consideration for optimal performance. In general, antennas
radiate and receive best perpendicular to the direction they point. Thus a vertical antenna's radiation
pattern is strongest across the horizon. Metal objects near the antenna may impede the radiation
pattern. Metal objects between the transmitter and receiver can block the radiation path or reduce
the transmission distance, so antennas should be positioned away from them when possible. Some
objects that are often overlooked are metal poles, metal studs or beams in structures, concrete (it is
usually reinforced with metal rods), vehicles, elevators, ventilation ducts, refrigerators, microwave
ovens, batteries, and tall electrolytic capacitors. If the XBee is to be placed inside a metal enclosure,
an external antenna should be used.
XBee units with the Embedded PCB Antenna should not be placed inside a metal enclosure or have
any ground planes or metal objects above or below the antenna. For best results, place the XBee at
the edge of the host PCB on which it is mounted. Ensure that the ground, power and signal planes
are vacant immediately below the antenna section. We recommend allowing a “keepout” area, which
is shown in detail on the next page.
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